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Trisomy 18

(Edwards Syndrome; Trisomy E)


Nina N. Powell-Hamilton

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Reviewed/Revised Nov 2023
Topic Resources

Trisomy 18 is a chromosomal disorder caused by an extra chromosome 18 that results in intellectual disability and physical abnormalities.

  • Trisomy 18 caused by an extra chromosome 18.

  • Infants are typically small and have many physical abnormalities and problems with internal organs.

  • Tests can be done before or after birth to confirm the diagnosis.

  • There is no cure for trisomy 18.

An extra chromosome, making three of a kind (instead of the normal two), is called trisomy. Children who have trisomy 18 have a third chromosome 18.

Trisomy 18 occurs in about 4 out of 10,000 pregnancies. The extra chromosome almost always comes from the mother. Mothers who are over age 35 are at increased risk of having a child with trisomy 18. There are more girls than boys with trisomy 18.

Symptoms of Trisomy 18

In the womb, affected fetuses are not typically very active, and there is often excess amniotic fluid, a small placenta, and restricted growth.

Physical abnormalities

At birth, newborns often have a low birth weight and their muscles and body fat are underdeveloped. Newborns are typically limp and have a weak cry. The mouth and jaw may be small, which gives the newborn's face a pinched appearance.

The hands are clenched in fists, and the index fingers often overlap the middle and ring fingers. The fingernails are underdeveloped. Skinfolds, especially over the back of the neck, are common. The big toes are shortened and frequently bend upward. Clubfeet Clubfoot and Other Foot Defects Clubfoot (talipes equinovarus) is a birth defect in which the foot and ankle are twisted out of shape or position. Birth defects, also called congenital anomalies, are physical abnormalities... read more Clubfoot and Other Foot Defects and rocker-bottom feet are common.

Other visible deformities are common, including a small head, low-set and malformed ears, a narrow pelvis, and a short breastbone (sternum).

Physical abnormalities may be obvious at birth. However, some newborns have abnormalities that are not as obvious.

Common Types of Clubfoot

Common Types of Clubfoot
Characteristic Physical Features of Trisomy 18

Internal abnormalities

Diagnosis of Trisomy 18

  • Before birth, ultrasonography of the fetus or blood tests of the mother

  • Before birth, chorionic villus sampling, amniocentesis, or both

  • After birth, the appearance of the infant and blood tests of the infant

Before birth, trisomy 18 may be suspected based on findings detected during an ultrasound of the fetus Ultrasonography Prenatal testing for genetic disorders and birth defects involves testing a pregnant woman or fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including... read more . Doctors also can do a test to find deoxyribonucleic acid (DNA) from the fetus in the mother's blood and use this DNA to detect an increased risk of trisomy 18. This test is called noninvasive prenatal screening (NIPS) or cell-free fetal DNA analysis.

After birth, the infant's physical appearance may suggest the diagnosis of trisomy 18. To confirm the diagnosis of trisomy 18, the infant's chromosomes typically are analyzed using a blood test.

Treatment of Trisomy 18

  • Support for the family

There is no cure for trisomy 18.

Children with trisomy 18 have severe developmental delay and disability. They should receive physical and speech therapies starting early. It is recommended that family members seek support.

Treatment of some of the abnormalities caused by trisomy 18 has resulted in some people living longer. These people are at increased risk of developing certain tumors, such as in the liver (hepatoblastoma Hepatoblastoma Primary liver cancers are cancers that originate in the liver. The most common is hepatocellular carcinoma (hepatoma). At first, liver cancer usually causes only vague symptoms (such as weight... read more ) and kidneys (Wilms tumor Wilms Tumor Wilms tumor is a specific kind of kidney cancer that occurs mainly in young children. The cause of Wilms tumor is not known, but some children may have a genetic abnormality that increases their... read more ). To help detect these tumors and other complications, doctors may recommend that children have periodic blood tests and imaging studies such as ultrasonography of the abdomen and kidneys.

Prognosis for Trisomy 18

More than 50% of children die within the first week, and only 5 to 10% are still alive at 1 year of age. However, recently, people who have trisomy 18 are living longer, and there are adults with trisomy 18.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

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